Here's my take on the different clay bars: they usually fall into one of three categories for me.
1) Soft, pliable, conforms easily, folds easily, picks up contaminants and "grabs" them, generally a pleasure to use.
2) Hard, "elasticky", bendable, slightly tough, picks up contaminants and "holds" them, somewhat less pleasureable to use.
3) Rock hard or soft and crumbly, hard to work with, streaks, binds and grabs, "drags" on surface, not fun to use.
I've tried (in alphabetical order): 3M,
Clay Magic, Eagle One, Formula113, Griots,
Meguiar's, Mothers,
Pinnacle and Zaino clay. If you ask me, I think that a lot of these clays come from the same place - they're so similar in a lot of ways.
That said, my very favorite clay is Clay Magic clay. It fits the #1) description above perfectly. Most of the others fit the #2 and only a very few fit the #3 description.
Just to complicate matters, many of the clays come in different levels of abrasiveness...generally speaking, for our uses/needs, stick with the "finest" or "gentleist" (word?) clay. For Clay Magic, I use their blue bars (fine), but I have a few of the red (med) bars too...HTH!